Compounds having a large absorption in a range of 500 to 700 nm, particularly those having a maximum absorption (λmax) in a range of 550 to 620 nm are used as optical elements including a recording layer of optical recording media, such as DVD-Rs, and an optical filter of image displays, such as liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescence displays (ELDs), cathode ray tube displays (CRTs), fluorescent tube displays, and field emission displays.
For applications to the optical elements, a number of cyanine compounds having an indole ring which have high sensitivity have been studied. There have been made many reports on this type of cyanine compounds particularly for their capability of coping with increasing recording speeds in applications as a recording element in optical recording media represented by DVD-Rs. Among them are Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4 (hereinafter referred to as references-1 to 4). References-1 to 3 disclose cyanine compounds which may have an aralkyl group at the 3-position of the indole ring. While these compounds are analogous to the cyanine compound of the present invention, the references are silent on the method and effects of introducing an aralkyl group to the cyanine compound. Additionally, these and other known cyanine compounds are unsatisfactory in thermal decomposition characteristics. In optical recording material applications, compounds having low decomposition temperatures are suited. The cyanine compounds described in references-1 to 4 are not satisfactory in this aspect, nevertheless.    Patent Document 1: JP-A-10-278426    Patent Document 2: JP-A-11-227331    Patent Document 3: JP-A-11-277904    Patent Document 4: JP-A-2002-52829